Add another row at the bottom of the report, and give it an expression along the lines of:

=First(Fields!FieldName.Value, "DataSet2")

Where DataSet2 is the dataset containing the second query.

Can't remember the exact syntax. If you use the expression builder at the bottom of the expression pop up (use Datasets->etc etc) it should generate the correct syntax.

There's probably a way to do it all in one query using ROLLUP but I'm not particularly good with that clause!

Edit:

Can also be done with UNION, might be easier than multiple datasets:

select

property_name,

count(distinct lead_id) AS leads_sent,

1 as OrderField

from leadtracker

group by property_name

union all

select 'Total', sum(DistinctLeads), 2

from

(

select

property_name,

count(distinct lead_id) as DistinctLeads

from leadtracker

group by property_name

) dl

union all

select 'Total Unique Leads', count(distinct lead_id), 3

from leadtracker

order by OrderField, PropertyName